Evaluation of fracture healing is normally based on physical and roentgenographic findings. Such evaluation is subjective and, at times, may be misleading. For example, slight motion is difficult to detect and tenderness may be difficult to interpret. Abundant callus may give a misleading roentgenographic appearance of greater strength than is actually present. Because the rate of union is variable, knowledge of elapsed time since fracture does not afford precise estimation of union in individual cases. Thus, a method for nondestructive evaluation of fracture union is desirable. However, various present techniques either have severe limitations or are invasive. We propose to test the usefulness of measurements of the frequency of mechanical resonance and the driving point mechanical impedance of fractured bones as an index of healing. We will validate these methods by measuring cadaver bone specimens and correlating the measured resonant frequency and mechanical impedance with the bone strength. Periodic measurements ill be obtained in dogs following tibial osteotomy for further validation. We will also repeatedly measure bone resonant frequency and mechanical impedance of several sites in the appendicular skeletons of approximately 50 patients with tibial and femoral fractures. This study will allow empirical validation of the resonant frequency and impedance techniques as well as test the predictive value of these methods for estimating healing rates of individual patients. Such studies may ultimately allow accurate determination of the time when immobilization is no longer required. The program will form a pool of baseline data for comparing the utility of different methods of fracture treatment such as patellar tendon bearing casts, cast braces, etc. It would also allow future testing of drugs which might influence fracture healing.